This research asks how concepts and larger causal beliefs systems, known as theories, interact in development. In doing so, it also asks how such patterns of development are relevant to general models of conceptual structure. One set of studies documents the development of coherent theoretical beliefs in the domain of biological thought. These studies show how different sets of properties may be most critical to the identity of biological kinds at different points in the preschool and elementary school years, and ask whether the youngest children use coherent biological theories to organize kinds or more general atheoretic metrics of similarity. These patterns of development are then contrasted to emerging knowledge of other biological phenomena such as inheritance, mechanisms of growth, disease, and physiology, with specific predictions about differing ways in which these areas of knowledge should be related. Other studies explore how relations between emerging theories and conceptual structure differ in natural kinds and artifacts. Among other tasks, children make inductions about properties, and explain malfunctions, anomalies and correlations. They are also presented with complex artifacts and engineered natural kinds so as to show how the distinctions between these two areas can become blurred. Finally, three studies test the more general model of conceptual and theoretical change as well as looking for certain biases in the causal beliefs underlying natural concepts in adults.